Solid caustic treatment of hydrocarbons



United States Patent SOLID CAUSTIC TREATMENT OF HY DROCAREONS Lewis M. Browning, Jr., Woodbury, and Raymond M. Kaulfrnan, Haddon Heights, N. L, assignors to Socony Mobil Oil Company, Inc., a corporation of New York No Drawing. Application December 26, 1951, Serial No. 263,464

Claims. (Cl. 196--32) The present invention relates to the treatment of hydrocarbons to remove acidic organic materials therefrom and, more particularly, to the treatment of hydrocarbons with finely divided solid alkali metal hydroxide to remove mercaptans therefrom. The present invention relates especially to the activation of finely divided solid alkali metal hydroxide whereby the extractive ability of the finely divided solid alkali metal hydroxide is enhanced and to methods of treating finely divided solid alkali metal hydroxide to secure said activation. 7

The problem of removing acidic organic materials an particularly mercaptans from hydrocarbon mixtures has received considerable attention in recent years. In general, removal of mercaptans from mixtures of hydrocarbons is accomplished by extracting the mercaptans from the hydrocarbon mixture with a solution of alkali metal hydroxide. Initially, aqueous solutions of sodium or potassium hydroxide were used. The extractive ability of such aqueous solutions was improved later by the addition of organic compounds, known to the art as solutizers, such as isobutyric acid, tannic acid, naphthenic acids and cresols. In March 1944 Edwin R. Birkhimer was issued U. S. Patent No. 2,345,449 disclosing that, while aqueous solutions containing 35 to 50% sodium hydroxide were efiective in extracting mercaptans from mixtures of hydrocarbons, the use of such aqueous solutions was attended by a disadvantage. That is to say, it was disclosed in this patent that aqueous solutions containing 35 to 50% sodium hydroxide tend to solidify at ordinary temperatures. The patentee dis-. closed that this disadvantage can be overcome by adding 2 to 10 volume per cent of a water-soluble organic solvent such as methanol, ethanol, isopropanol, ethylene glycol, propylene glycol or glycerol to the aqueous caustic solution.

1 In U. S. Patent No. 2,311,593 Kalichevsky et a1. disclose the use of colloidal particles of alkali metal hydroxides for the removal of weakly acidic sulfur compounds such as mercaptans from hydrocarbon mixtures such as petroleum fractions. These patentees define colloidal particles as those having a diameter between 0.00001 centimeter and 0.0000001 centimeter.

The present invention is directed particularly to an improved method for removing weakly acidic sulfur compounds such as mercaptans from mixtures of hydrocarbons employing activated finely divided particles of solid alkali hydroxide and to a method of activating such a reagent for the removal of weakly acidic sulfur compounds from mixtures of hydrocarbons.

It is an object of the present invention to provide a method for the removal of weakly acidic organic material from mixtures of hydrocarbons employing activated finely divided solid alkali metal hydroxide as the extracting agent.

It is another object of the presentinvention to provide a method of activating finely divided solid alkali metal hydroxide for use as an extracting agent in the removal of the diameter thereof, having a temperature of at least.

"ice

of weakly acidic organic material from mixtures'of hydrocarbons.

It is a further object of the present invention to provide a method of producing activated finely divided solid alkali metal hydroxide from a solution of said alkali metal hydroxide. I

It is also within the scope of the present invention to provide a method of removing mercaptans from mixtures of hydrocarbons employing activated finely divided solid alkali. metal hydroxide as the extracting agent.

Other objects and advantages will become apparent to those skilled in the art from the following discussion.

As disclosed by Kalichevsky et al. in U. S. Patent No. 2,311,593, Anhydrous sodium hydroxide is capable of removing quantitatively mercaptans from petroleum oils provided sufiicient time is allowed for completing the reaction. With some gasolines containing higher mercaptans from two to twenty-four hours of continuous agitation may be necessary to sweeten the gasoline, depending on the state of subdivision of the reagent. In addition, the surface of the sodium hydroxide particles is quickly coated with the adsorbed layer of mercaptides, thus preventing further reaction. For this reason, the quantity of sodium hydroxide required to sweeten gasoline is much greater than theoretical. We have found that both the time of the reaction and the quantity of sodium hydroxide required for sweetening gasoline depends primarily on the surface of sodium hydroxide exposed to gasoline .rather than on the total quantity of sodium hydroxide present. These patentees then state that the maximum diameter of particles of alkali metal hydroxide used for the purpose of removing mercaptans from a gasoline containing 0.0092% mercaptan sulfur in 30 minutes should not. be greater than-0.000048 centimeter. However, in general the particles of finely divided solid anhydrous alkali metal hydroxide should be of colloid .size,i. e.,.the particles should have diameters between 0.00001 centimeter and 0.0000001 centimeter.

While. these patentees indicate a preference for finely divided solid anhydrous alkali metal hydroxide in which the particles have diameters between 0.00001 and 0.0000001 centimeter, it has been found thatparticles of activated alkali having diameters of about 0.0001 to about 0.004 centimeter, i. e., 1 to 40 microns are very effective for the removal of acidic organic material, especially. mercaptans from hydrocarbons and mixtures of hydrocarbons. e

As disclosed in the. aforesaid U. S- Patent No. 2,311,593, colloidal particles of solid anhydrous alkali metal hydroxide suitable for the extraction of weakly acidic organic material such as mercaptans from mix-- tures of hydrocarbons can be prepared by the use of colloidalj mills, electric arc, deposition of thin layers of solid anhydrous alkali metal hydroxide on inert materials possessing high surface areas or by spraying moltenanhydrous alkali metal hydroxide into gasoline. However, it is preferred to produce the finely divided solid anhydrous alkali metal hydroxide by the method disclosed in co-pending application Serial No. 263,461 filed co-pending application comprises establishing a column of water-immiscible liquid having a heightseveral'multiples the boiling point of mixture of alkali solution and said water-immiscible liquid, introducing an aqueous alkaline solution into said water-immiscible liquid in the form of immiscible liquid as the continuous phase, agitating said suspension vigorously, raising and maintaining the. temperature of the mixture of said water-immiscible liquid and alkali solution at the boiling point thereof at the pressure existing above said column of liquid by introducing heated vapors of said water-immiscible liquid into said column, whereby water is evaporated from said droplets of aqueous solution and the droplets become more dense and gravitate to the bottom of said column of liquid,"- and cooling the suspension of small particles of solid alkali metal hydroxide :in said water-immiscible liquid to temperatures below the melting point of said particles of alkali metal hydroxide. The particle size of the solid alkali metal hydroxide produced in this manner can be i. e., between 1 and40 microns, can be activated by the hereindescribed method to provide an effective means for the removal of weakly acidic organic material from a hydrocarbon mixture.

5 Illustrative of the effect of activation is the treatment of a slurry of an alkali metal hydroxide, caustic soda, to activate the same and the use of the activated caustic soda in removing weakly acidic organic material, e. g., mercaptans from a hydrocarbon mixture, gasoline. The data 10 set forth in Table I was obtained treating a slurry of finely divided anhydrous sodium hydroxide with the quantities of methanol indicated and then treating, in a single stage extraction, an isooctane.

Table l Do2s0%g7e at Extraction 4 Percent ggg Theofy, Percent Run 1N0. in NaOH Lbs. Original RSH-S in RSH-S Particles NaOH NaOH/l,(100 RSH-S, Effluent, Removed Bbls. Percent Percent Mixture W Wt.

97. 5 None 718 0. 112 0. 0190 83 100 1 :N one 614 0. 006 0. 0079 91. s 99 R 3 640 0. 100 0. 0032 96. 8 87 2 640 0. 100 0. 0032 96.8 92. Z 10 630 0. 099 0. 0028 97. 2 90 10 589 0. 092 0. 0016 98.3 95 2 12 040 0.100 0. 0043 95. 7 v100 2 24 640 0. 100 0. 0064 93. 6 100 1 .48 640 0. 100 0. 0256 74. 4 .93. 5 4 None 640 0. 100 0. 0425 57. s 100 .6 640 .0. 100 0. 0077 92. 3 100 1 1. 2 608 0. 095 0. 0195 .79. 5 100 1 0.5 608 0. 095 0. 0455 52.1 92 K 0. 12 V .608 0. .095 0. 0500 47. 4

l Bums 1 through 9 made, with difi'erent caustic samples than were Runs 10 through 14. Slurry washed with dried benzene before addition of methanol.

3 Treated with 10 gallons of methanol/lflflpounds of NaOH and redistilled.

4 Single stage extraction of isooctane-u-butyl mercaptan mixture.

controlled by, the concentration of the alkali metal hydroxide solution charged and the manner in which it is charged.

vBroadly .stated,.the method .of removing weakly acidic organic .material such .as mercaptans from mixtures of hydrocarbons comprises bringing the mixture of hydrocarbons .to he treated into intimate contact with finely divided solid anhydrous alkali metal hydroxide activated as described hereinafter. The actual physical means by which intimate contact between the particles of solid anhydrous alkali metal hydroxide and the mixture of hydrocarbons to be treated is achieved is not of paramount importance. For example, the hydrocarbons to "be treated can be placed in a container provided with an agitator, an inlet for particles of :solid anhydrous alkali metal hydroxide and means for .removing the treated hydrocarbons and :the exhausted alkali metal hydroxide. Alternatively, theparticles of .solid anhydrous alkali metal hydroxide canbe rfied .into the top of .a .column and the hydrocarbons 10 be treated .can be introduced into that column .at a point near .the :bottom thereof and'intimate contact provided by the hydrocarbons rising in the column while'the particles of alkali metal hydroxidedescendto be drawn voif rat the lower end .of the column while the treated hydrocarbons are withdrawn at the upper end of the column.

Thefinelyxdividedsolid anhydrous alkali metal hydroxide. can be activated by making a slurry of the particles of solid anhydrous .caustic in .a treated hydrocarbon or an organic material readily separated from the hydrocarbon to .be .treated and adding to the :slurry about 3 to about 6 gallons. of an aliphatic monohydric alcohol .per' 100 pounds of alkali metal hydroxide in .said slurry.

It is of interest to note that while Kalichevsky .et al. found that .it was preferable to use partidles .of .alkali metal hydroxide having diameters; between 05100011 and Q.QOQ0.001 centimeter and not greater than-.0;(l0.0048.centimeter in diameter, itlias mow beeniound that particles havingdiameters, between 0300.01 and -0;004 icentimeter,

Inspection of .the data presented in Table I makes it apparent that treatment with 0.12 to 1.2 gallons of methanol has little activating efiect upon the extractive ability of the particles of solid caustic. At 3 gallons of methanol per pounds of .NaOH activation takes place. The use .of ,10 gallons of methanol per 100 pounds of NaOH produces further improvement in the extractive ability of the caustic but dosages at levels in excess of 10 gallons per 1 00 pounds of NaOH do not provide greater efiects. ,In fact, at the level of 24 gallons of methanol per 100 pounds .NaOH and above there is indication that the effectiveness of the caustic is decreased. It will be noted that treatment of the slurry .of particles of solid caustic with .10 gallons of methanol per 100 .pounds of NaOH and ,redistillation of the slurry provided enhanced extractive capacity as compared to activation with the same quantity of methanol but not followed by redistillation.

It has been toundxthat when an alkali metal hydroxide such -as .caustic :soda is dissolved in an aliphatic monohydric alcohol and the solution so formed dehydrated by boiling with .a nonmiscible liquid such as a Ehydrocarbon, for example, isooctane .or a mixture of hydrocarbons such as gasoline or kerosene, the particles of caustic so produced have satisfactory extraction .efficiencies without further treatment. Because of the ease with which alcohol can be removed from the caustic in solution .as compared to removing water, distillation is carried out at a much lower temperature than when dohydrating caustic from aqueous solutions. At any specified boiling temperature the ratio .of alcohol to hydrocarbon vapors in the overhead from the distillation is much higher than the ratio of water to hydrocarbon 'in the overhead from the distillation of aqueous caustic solutions.

Instead of dissolving the alkali metal hydroxide in methanol and dehydrating the caustic, an aliphatic monohydric alcohol can be added to a slurry of finely divided solid anhydrous caustic in a water-immiscible liquid and the mixture distilled to drive off the alcohol. The resulting slurry of finely divided solid anhydrous caustic has better extraction characteristics than it had before the addition of the alcohol or before distillation. (Vide Table I, Runs and 6.)

Illustrative of the use of aliphatic mono-hydric alcohols having not more than about 5 carbon atoms for activating finely divided solid anhydrous alkali metal hydroxide are the data presented in Table II.

hydroxide as described and set forth in claim 3 wherein the aliphatic mono-hydric alcohol is methanol and the alkali metal hydroxide is sodium hydroxide.

6. A method of removing weakly acidic organic material from hydrocarbon admixed therewith which comprises mixing a slurry of particles of anhydrous alkali metal hydroxide having diameters of about 1 to about 40 microns in a non-aqueous liquid with at least 3 gallons per 100 pounds of alkali metal hydroxide of an 1 Produced by precipitation from methanol solution. 9 Single stage extraction of isooctane-n-butyl mercaptan mixture.

While theoretically the amount of alkali metal hydroxide required to remove a given amount of weakly acidic organic material such as mercaptans from ad mixture with a hydrocarbon or hydrocarbons is the molecular equivalent of the weakly acidic organic material, it has been found that an amount of alkali metal hydroxide in excess of the stoichiometric amount must be used for practical purposes. From a consideration of the various factors it is preferred to use 200% and with certain gasolines 400%, of the theoretical amount required to form the alkali metal hydroxide salt of the acidic material such as mercaptans. Greater amounts can be used but at the cost of diminishing returns. Lesser amounts can be used with some disadvantages.

We claim:

1. A method of removing mercaptans from gasoline which comprises adding about 3 to about 10 gallons of an aliphatic mono-hydric alcohol having not more than five carbon atoms per molecule per 100 pounds of alkali metal hydroxide to a suspension of particles of alkali metal hydroxide having diameters of about 1 to about 40 microns in a non-aqueous liquid, boiling the resulting suspension to remove said alcohol and obtain a suspension of activated particles of solid alkali metal hydroxide, contacting said suspension of activated particles of alkali metal hydroxide with gasoline containing mercaptans, and separating treated gasoline from particles of solid alkali metal hydroxide.

2. The method of removing mercaptans from gasoline as set forth and described in claim 1 wherein the aliphatic mono-hydric alcohol is methanol and the alkali metal hydroxide is sodium hydroxide.

3. A method of producing activated finely divided solid alkali metal hydroxide which comprises introducing a solution of alkali metal hydroxide in an aliphatic monohydric alcohol having not more than five carbon atoms per molecule into a boiling non-aqueous liquid having a boiling point higher than that of said alcohol, dispelling said alcohol to form particles of solid anhydrous alkali metal hydroxide having diameters of about 1 to about 40 microns, and cooling said particles of anhydrous solid alkali metal hydroxide below the melting point thereof to obtain activated particles of solid anhydrous alkali metal hydroxide having diameters of about 1 to about 40 microns.

4. The method of activating finely divided solid alkali metal hydroxide described and set forthin claim 3 wherein the alcohol is methanol.

5. The method of activating finely divided alkali metal aliphatic monohydric alcohol having not more than 5 carbon atoms per molecule to obtain activated particles of anhydrous alkali metal hydroxide having diameters of about 1 to about 40 microns, separating said alcohol from said slurry of particles in non-aqueous liquid, contacting a mixture of hydrocarbon and weakly acidic organic material with said slurry to extract said weakly acidic material and to obtain treated hydrocarbon and separating treated hydrocarbon from the slurry of activated particles of alkali metal hydroxide contaminated with extracted weakly acidic organic material.

7. The method of removing weakly acidic organic material from hydrocarbon admixed therewith as set forth and described in claim 6 wherein the non-aqueous liquid is of the nature of treated gasoline, and the mixture of hydrocarbon and weakly acidic organic material is gasoline containing mercaptans.

8. A method of removing mercaptans from gasoline which comprises dissolving an alkali metal hydroxide in a monohydric aliphatic alcohol having not more than five carbon atoms per molecule, mixing alcoholic solution with treated gasoline, raising the temperature of said mixture to a temperature above the boiling point of said mixture to remove said alcohol and to obtain a suspension of activated particles of anhydrous alkali metal hydroxide having diameters of about 1 to about 40 microns in said treated gasoline, contacting said suspension of activated particles of alkali metal hydroxide with gasoline containing mercaptans 'to extract mercaptans therefrom and to obtain treated gasoline, and separating treated gasoline from particles of alkali metal hydroxide contaminated with extracted mercaptans.

9. The method of removing mercaptans from gasoline as described and set forth in claim 8 wherein the alkali metal hydroxide is sodium hydroxide.

10. The method of removing mercaptans from gasoline as described and set forth in claim 8 wherein the aliphatic monohydric alcohol is methanol.

References Cited in the file of this patent UNITED STATES PATENTS 1,935,725 Perl Nov. 21, 1933 1,970,583 Stagner Aug. 21, 1934 2,538,287 Voorhees Jan. 16, 1951 2,546,345 Meadows et al. Mar. 27, 1951 2,578,602 Rosenstein Dec. 11, 1951 2,596,175 Rosenstein May 13, 1952 2,641,572 Meadows et al June 9, 1953 

1. A METHOD OF REMOVING MERCAPTANS FROM GASOLINE WHICH COMPRISES ADDING ABOUT 3 TO ABOUT 10 GALLONS OF AN ALIPHATIC MONO-HYDRIC ALCOHOL HAVING NOT MORE THAN FIVE CARBON ATOMS PER MOLECULE PER 100 POUNDS OF ALKALI METAL HYDROXIDE TO A SUSPENSION OF PARTICLES OF ALKALI METAL HYDROXIDE HAVING DIAMETER OF ABOUT 1 TO ABOUT 40 MICRONS IN A NON-AQUEOUS LIQUID, BOILING THE RESULTING SUSPENSION REMOVE SAID ALCOHOL AND OBTAIN A SUSPENSION OF ACTIVATED PARTICLES OF SOLID ALKALI METAL HYDROXIDE, CONTACTING SAID SUSPENSION OF ACTIVATED PARTICLES OF ALKALI METAL HYDROXIDE WITH GASOLINE CONTAINING MERCAPTANS, AND SEPARATING TREATED GASOLINE FROM PARTICLES OF SOLID ALKALI METAL HYDROXIDE. 